Communication packets often include error detection information such as checksums that are used by receiving nodes in a network to verify the integrity of information in received communication packets. In some situations, an intermediate node in a network that processes a communication packet modifies contents of the communication packet. For example, the intermediate node may modify a timestamp field, a time delay field, a hop count field, a time-to-live (TTL) field, etc. Although integrity of the communication packet remains otherwise sound, the modified field will invalidate the checksum. In some prior art systems, when modifying a field of a packet invalidates a checksum in the packet, the checksum field is set to a value of zero to avoid an erroneous error indication, which causes the receiving device to ignore the checksum value. Thus, the receiving device is unable to verify the integrity of the received communication packet using the checksum field.
U.S. Pat. No. 8,948,037 describes a method for adding a checksum trailer to a packet when a timestamp field in the packet is modified. For example, in one embodiment described in U.S. Pat. No. 8,948,037, a checksum trailer value is determined to maintain correctness of a checksum field in the packet after the timestamp field has been modified, and a padding field of the packet, separate from the checksum field, is set to the checksum trailer value.